In typical PTCA procedures, a guiding catheter is percutaneously introduced into the cardiovascular system of a patient and advanced through the aorta until the distal end is in the ostium of the desired coronary artery. Using fluoroscopy, a guide wire is then advanced through the guiding catheter and across the site to be treated in the coronary artery. An over the wire (OTW) balloon catheter is advanced over the guide wire to the treatment site. The balloon is then expanded to reopen the artery. The OTW catheter may have a guide wire lumen which is as long as the catheter or it may be a rapid exchange catheter wherein the guide wire lumen is substantially shorter than the catheter. Alternatively, a fixed wire balloon may be used. This device features a guide wire which is affixed to the catheter and cannot be removed.
To help prevent arterial closure, repair dissection, or prevent restenosis, a physician can implant an intravascular prosthesis, or a stent, for maintaining vascular patency inside the artery at the lesion. The stent may either be a self-expanding stent or a balloon expandable stent. For the latter type, the stent is often delivered on a balloon and the balloon is used to expand the stent. The self-expanding stents may be made of shape memory materials such as Nitinol or constructed of regular metals but of a design which exhibits self expansion characteristics.
An exemplary stent delivery catheter is disclosed in commonly assigned U.S. Pat. No. 5,772,669 to Vrba. The Vrba catheter has a retractable distal sheath concentrically arranged around a stent and a pull back means operatively connected to the distal sheath. The catheter is constructed and arranged such that at least the proximal end portion of the retractable sheath is received inside an outer body portion of the catheter on retraction of the sheath. In retracting the sheath, a length of sheath in excess of the length of the stent is moved. In the process of retracting the sheath, there is typically a frictional interaction between the sheath and the vessel wall.
In a catheter having a full length sheath, the frictional interaction between the sheath and the vessel wall may become more significant, possible resulting in motion of the distal end of the catheter relative to the vessel wall which, in turn, may result in decreased accuracy in the deployment of a stent.
For the purpose of this disclosure, all US patents and patent applications and all other publications referenced herein are incorporated herein by reference in their entirety.
It is desirable to provide a medical device deployment catheter having improved deployment accuracy. Such a device may be provided in the form of a catheter in which the length of those portions of the catheter which are in contact with a vessel and which move on deployment of the medical device are of reduced length.
To that end, the present invention in one embodiment is directed to a stent delivery catheter comprising a guidewire lumen for receiving a guidewire therein. A stent is disposed about the distal end of the guidewire lumen and is covered by a retractable sheath disposed about the distal end of the guidewire lumen. The retractable sheath may be retracted by pulling on a pullwire in mechanical communication with the retractable sheath. The pullwire is disposed within a pullwire lumen. A slit of a predetermined length is provided in the pullwire lumen to allow for egress of the pullwire. The distal end of the pullwire extends from the pullwire lumen at the slit.
In another embodiment, the invention is directed to a medical device delivery catheter which comprises an inner tube with a medical device bearing region at the distal end. A retractable sheath is disposed about the medical device bearing region of the inner tube. The retractable sheath is controlled by a pullwire which is in mechanical communication with the retractable sheath. The pullwire extends proximally therefrom and is carried in a pullwire lumen. A slit is provided in the pullwire lumen for egress of the pullwire therefrom. The length of the slit exceeds the length of the medical device to be delivered. Desirably, the length of the stent will be approximately equal to the length of that portion of the retractable sheath which extends from the proximal end of medical device bearing region of the catheter and terminates at the distal end of sheath.